1. Field of the Invention
The present invention relates generally to high-speed reproduction or playback of an image signal recorded on a video tape recorder (VTR) tape through conversion of an image produced at twenty-four (24) frames per second to an image of sixty (60) fields/second. More particularly, but not exclusively, this invention relates to a high-speed image reproduction method and apparatus for reproducing only a specific predefined image or images at an increased speed 2.5 times greater than the standard playback speed, which images are selected from among those of two fields and three fields recording therein a single video frame, respectively.
It should be noted that although in the currently available NTSC standard scheme, the number of successive fields per second in televisions is precisely set at 59.94 (59.94 fields/second) and in a high definition television (HDTV) environment--such as the "High-Vision" system in Japan--the number could be a mixture of 59.94 and 60, these are collectively called the "60 fields/second". Accordingly, it is to be understood that the term "60 fields/second" as will be used herein refers to either 59.94 fields/second or 60 fields/second.
2. Description of the Related Art
Currently, component signals for use in broadcasting and composite signals such as NTSC, PAL or the like are typically subject to interlace (interlaced scanning) processing. In the NTSC system, video frame images are at the rate of 30 pieces per second whereas field images are at 60 pieces/second. Animations and motion pictures are generally photographed and filmed at the rate of 24 frames/second. Accordingly, one prior known approach to record such original images on a VTR tape is to first convert the initial one picture frame into two video fields while converting the next frame to three fields, repeat this procedure consecutively, thereby perform conversion to video images of 60 fields/second by what is called the "two-to-three (2-3) pull-down" technique, and then record them on the VTR tape.
As digital VTRs including "D-2" or "D-3" VTRs, currently available VTRs come with a function of thinning out video fields at constant intervals in conformity with a playback speed when reproducing a video signal from N recording tracks (where "N" is a predetermined natural number) that have been recorded on a tape in a manner corresponding to field images by use of an auto-tracking (AT) head movable in the track width direction in units of N tracks corresponding to the field images, thereby outputting the reproduced video signal.
Considering one exemplary case of high-speed reproduction at an increased speed that is, for example, 2.5 times the standard playback speed--say, 2.5.times.quick playback--as implemented in the present invention, the above function of the conventional VTRs is achieved by setting the tape feed speed at a value 2.5 times greater than the standard feed speed, and sequentially repeating a playback procedure which includes playing back a field image that essentially consists of N tracks recorded on a tape while thinning out a single field and then thinning out two fields. However, a problem may occur in that one or more picture frames fail to be played back or "skipped" during the high-speed reproduction unless a deeper appreciation is given to the exact relation between one "frame" or "picture" of the original image (i.e. a one-scene picture on motion picture films) and a plurality of video fields of the image signal thus converted.
As noted above, in the conventional VTRs' high-speed or quick playback function, achievability of the 2.5.times.quick playback does not come without accompanying a penalty--it has been impossible to intentionally select any desired fields. Thus, during reproduction of VTR tapes which record thereon video images through conversion from 24-frames/second images to 60-fields/second ones, it has been impossible, or at least greatly difficult, to select a single field from a group of two successive fields with one picture recorded therein and also one field from a group of three fields recording therein one picture, and then play back only images of such selected fields at high speeds.